Echo sounding indicator



F. n.. SEEBINGER, J

ECHO SOUNDING INDICATOR Fld March 10, 1945 \N\ wk mm man.: 2.5.55 @2 52. Q2

llllllllllll IIIIIIIIIIIJ NN. NQ SW Patented Aug. l0, 1948 UNITED STATES PATENT GFFICE ECHO SOUNDING INDICATOR Fred L. Seebinger, Jr., Vallejo, Calif., assigner to International Projector Corporation, New York, N. Y., a corporation oi Delaware Application March 10, 1945, Serial No. 582,149

This invention relates to echo sounding and particularly to rapid and automatic water depth determination under a vessel.

In such art it is customary to transmit a signal from the vessel and obtain a. reflection back to the vessel from the sea bed the distance of which is to be determined. The interval of time between the transmission oi the signal and the reection back to the vessel gives an indication of the depth of the water under the vessel.

One object of the invention is to provide a lightweight and portable depth indicator which is sultable for war-time use in invasion barges and the like, and for peace-time use on fishing boats and other small craft.

Another object of the invention is to provide a continuous depth finder which does not require the use of motors, and includes novel means for measuring with a direct current meter, the time between the instant of transmission and the instant of receiving the rst echo.

A further object is to provide an electronic echo sounding instrument which can be operated from a battery as the only source of power, and which involves the use of small vacuum tubes.

A still further object of the invention is to provide a novel squelch circuit for inhibiting the undesired eect of direct communication between the transmitter and receiver in the water.

In accordance with the invention, for example, there is provided a portable instrument for the rapid, automatic determination of depths of water up to :a maximum distance, such as 100 feet, for example, below an outboard projector; comprising a pulse transmitter, an echo receiver, and means for indicating sea bed contour changes along the vessels course. The instrument generates supersonic sound pressure waves having a constant frequency of 25.0 kc., for example, at a predetermined constant rate of twelve per second, for example; projects the pulses downward; times them accurately in units of depth in their path of travel to the sea bed and return, by reection; and indicates the water depth directly in feet on a calibrated meter. Operation of the sounding indicator is entirely automatic.

The accompanying drawing is a diagrammatic view of an echo sounding circuit exemplifying the invention.

The illustrated circuit includes a sounding indicator I and an outboard projector P. The outboard projector P contains a magnetostrlction type oscillator transmitter T and receiver R in the same housing. The transmitter T converts the generated electrical impulses into sound pres- 2 sure waves and projects them downward to the "bottom," while the receiver R converts the reilected sound pressure waves into electrical impulses. 'Ihe outboard projector P is adapted to be swung over the side of the boat and positioned under the water line for observations.

'Ihe sounding indicator I is housed in a box containing an instrument panel Ill and an upper chassis I2 and a lower chassis It, all of which are arranged so as to be readily accessible. On the panel i0 are mounted a power switch I6, which controls the power supply from a six volt battery it to the entire unit: a depth indication meter 2t, which indicates the depth of water below the outboard projector directly in feet and is also used to check the battery and calibrate the instrument; a keying rate indicator 22, which indicates the sounding rate by a vibrating reed, for example; and a three-position test switch M.

The keying rate indicator 22 has five reeds, the center reed being designated by an arrow and the left and right outer reeds slow and fast, respectively, thereby indicating directly the keying rate per second -by the vibration of a reed. By adjusting a keying rate potentiometer 26 on the panel it and a potentiometer 2d, on the lower chassis it, the keying rate may be adjusted precisely to the predetermined constant value, in this case twelve pulses per second, which corresponds to maximum amplitude of the center reed. The keying rate potentiometer 2G provides for adjustment through rather narrow limits, additional adjustment being provided by the potentiometer 23. The keying rate should be accurately adjusted as any error in this adjustment affects the depth readings in the same proportion.

The three-position switch M is of the spring return type, being normally in the depth position for depth indications. In battery position, the charge of the battery i8 may be checked on the meter it. In calibration position, a calibration" potentiometer 30 on the panel may be ad.- i

justed, so that the pointer is in exact alignment with a predetermined mark. This adjustment should also be very carefully made, as any error f former 44; and associated resistor 46, inductors 48 and 60, and capacitors 62, 64 and 66 for filtering purposes. The output voltage of unit 32 is controlled by a voltage regulator tube 68 for all component circuits except the discharge circuit 36.

The sending of pulses, or keying, is controlled by that half of vacuum tube 60, which is associated with transformer 62, capacitor 64, resistor 66, and potentiometers 28 and 26. These elements comprise the vacuum tube oscillator 34, which would normally oscillate at an audio frequency. The circuit is so designed, however, that in endeavoring to oscillate the grid 68 draws current, develops a high negative bias and blocks itself. An impulse is transmitted each time this blocking takes place. The rate at which blocking occurs is adjustable by means of potentiometers 26 and 28 as previously described. Thus, by careful adjustment of these two potentiometers, the keying rate may -be accurately set at 12 pulses per second.

The other half of tube 60 amplies these pulses and transmits th'em simultaneously to the grids 10. and 12 of a grid-controlled gaseous-discharge tube (strobotron) 14, and a gas-filled grid-controlled rectier tube such as a thyratron 16. Each pulse on the grid of tube 14 hres or ionizes the gas in such tube, forming a conducting path from anode 18 to cathode 80 and thereby discharging a capacitor 82 therethrough and energizing the transmitting projector T. The thyratron 16 controls the voltage on the screen 84 of a screengrid amplifier tube 86 on the upper chassis I 2. At the instant the pulse is applied to the grid 12 of thyratron 16, it ionizes the gas in such tube, and the plate current ow through' thyratron 16 lowers the screen voltage on tube 86 by the IR. drop through an associated plate and screen resistor 88. When tube 16 fires, condenser 9 discharges through tube 16 and resistor 8, the condenser 9 and resistor 8 forming a delay network. At the same time the condenser 9 tends to recharge from the positive side of the power supply through resistor 86 but the time constant of the later circuit is so adjusted with respect to the time constant of the circuit consisting of resistor 8 and condenser 9 that the discharge current exceeds the charging current and the` anode potential of tube 16 is reduced to a point where the tube ceases to nre, the maximum current through the limiting resistor being insufficient to maintain an arc in tube 16. When tube 16 ceases to re condenser 9 is gradually charged through resistor 88 and the screen voltage of tube 86 is gradually returned to its original value, the time being determined by the time constant of the circuit consisting of resistor88 and condenser 8. This drop of short duration in screen voltage -reduces the gain of the receiver-amplifier 38 for said period of short duration so that a false indication of depth, due to direct transmission from th'e transmitting to the receiving projector, is avoided. The condenser 9 reacts on tube 86 in such a manner as to perform the functions of an automatic gain or volume control.

Crosstalk which would be indicated on the meter 20 as a steady very low depth reading regardless of the true depth of the water may be due to a variety of causes, such as, the direct transmission between transmitter T and receiver R, electrical coupling between the leads to the transmitter and receiver, reverberation in the housing of the outboard projector P and the like.'

For any particular installation, therefore, it is necessary to provide a control which will maintain the gain of tube 08 below a level which would transmit crosstalk until the eects which produce such Crosstalk have disappeared. To this end the potential of the cathode of tube 86 is made adjustable so that the relative potential between the cathodeV and screen grid, which relative potential constitutes the means for reducing the gain when signals are transmitted, may be varied to accommodate various situations that may arise.. This adjustmentis provided by the potentiometer ||6 in the cathode circuit of tube 68 which in adjusting th'e potential of the cathode with respect to ground likewise adjusts the relative potential existing between the cathode and screen grid. By proper adjustment the relative potential between cathode and screen grid may be so regulated that this potential does not rise to a value that would permit signals to be amplified by tube 86 until after the conditions which would produce Crosstalk have ceased. In other words, potentiometer ||6 adjusts the gain level and hence the crosstalk thresholdof tube 66. In practice an initial regulation of potentiometer ||8 for any given installation is all that is usually neces- Sary.

The three-stage receiver-amplifier 36 on the upper chassis l2 is tuned to a frequency of 25.0 kc., the natural period of the projectors T and R, by capacitors 90 to 96, inclusive, connected across the secondary |00 of an input transformer |02, and also by capacitors |03 and |04, connected across a second stage coupling inductor |06. Resistance coupling |08 is employed from the second to the third stage. The received electrical pulse, from the reected signal or echo, is amplied by amplifier tube 86 (its screen voltage returning to normal, as determined by the product of the resistance and capacitance in the plate circuit of tube-16, before the echo from deep water is received) and ampliiler tube ||0 and applied to the grid ||2 of ampliiier tube ||4.

Tube 4 is biased beyond cut-off, so that any extraneous noises will not give false depth indications, as several volts of signal are required for operation of the tube. Theplate voltage of tube 4 is the same, with respect to ground, as the grid voltage of a grid-controlled space disch'arge device or vacuum tube ||8 in the timer circuit 40. Therefore, as soon as tube ||8 ceases to draw plate current, as described below, the plate voltage of the ampler tube I4 is reduced to the extent that this latter tube is inoperative and even a very strong signal or any extraneous noises picked up by the receiver-ampliiier 38 will not cause false operation of the timing circuit 40.

Grid-controlled space discharge devices such as screen-grid vacuum tubes ||8 and 20 and l their immediately associated circuit elements, constitute the time measuring or trigger circuit 40. They measure the ratio of the time necessary for a pulse to be transmitted to the bottom and be reected back to the receiving projector, to the time between pulses. A potential of plus volts D. C., with respect to ground, is applied to the screens |22 and |24 of tubes ||8 and |20, and also to the junction |26 of resistors |28 and |30. The other end of resistor |28 is connected by conductors |32 and |34 through meter 20 to the plate |36 of tube ||8. The other end of resistor |30 is connected to the plate |38 of tube |20. Resistors |40 and |42 are connected in series circuit relation between the plate |38 of tube |20 and ground |44, the grid |46 of tube 8 being connected to their junction |48, and thus this grid |46 is positive with respect to ground. In a similar manner resistors |50 and |52 are in series between the plate side of resistor |28 and ground |66, and the grid |56 of tube |20 is connected to their Junction |56, so that this grid |54 is likewise positive with respect to ground.

Plate and screen currents of both tubes ||8 and |20 flow through the "calibratiom potentiometer 80 and a resistor |58 to ground |44, so that the cathodes |60 and |62 of both of th'ese tubes are also positive with respect to ground. Thus a trigger circuit 60 is provided, which permits only one of the plate or output circuits of tubes ||8 and |20 to draw current at a time. The resistor |58 is used to stabilize the voltage of cathodes |60 and |62 of tubes ||8 and |24. The grid of the other tube is biased beyond cut off until some disturbing voltage, such as that resulting from the transmitting pulse, or the "echo," upsets the balance and then the other tube draws plate current while the rst is biased oil. The potentiometer 30 is variable so that, when the tube |8 is drawing current, its plate current may be adjusted to a certain steady value, in this case two milliamperes. At all times the grids |46 and |56 of tubes ||8 and |20 are negative with respect to their cathodes |60 and |62.

When the instrument is in operation, tube |20 draws current during the short interval between receipt of the echo and the sending out of the next pulse and its grid |56 is slightly negative with respect to its cathode |62. At the same time, due to the IR drop through resistor |30, the grid voltage of tube ||8 is so low that this tube is biased beyond cut olf and draws no plate current. Also the plate voltage of amplifier tube I6 (which voltage is the same as the grid voltage .of tube M8) is so low that all signals are veffectively prevented from passing to the grid |46 of tube I I8.

The grid |54 of tube |20 is coupled to the anode .78 of the gas-filled tube 16 on the lower chassis I4 by means including capacitor |64 and resistors |66 and |68 so that a pulse on the anode 78 of tube 'M is impressed on the grid |54 of tube |20. This pulse, being ampliiied by tube |20, reduces the bias on the grid |46 of tube ||8 so that this tube ||8 begins to draw current. Due to the resulting IR drop through resistor |28, the voltage on the grid |56 of tube |20 is reduced so that this tube |20 is .biased beyond cut off and, therefore, ceases to draw current. The amplified received impulse, or echo is impressed on the grid ||2 of tube it, overrides its 4bias and since its plate voltage is normal the tube draws current. The echo pulse then passes to the grid |66 of tube I8, is amplified by such tube and impressed on the grid |54 of tube |20. The pulse reduces the grid bias on tube |20, and the tube |20 begins to draw current immediately. Tube 8 then is immediately biased olf, as previously described, and ceases to draw current. Thus, the circuits are established for the next pulse from the anode 18 of tube 7|.

At the instant tube |8 begins to draw current, its plate current of 2 milliamperes flows through meter 20 and at the instant the received pulse is impressed on the grid |66 of tube I8 this current ceases to flow, Thus, current flows through the meter 2li only during the interval of time required for the transmitted signal to reach the bottom and be reected back to the receiver R. The average value of the plate current of tube I8 over a series of successive energizations thereof is, therefore, proportional to depth. In the present example, for a depth of 100 feet this average value is l milliampere, for 50 feet it is 0.5

milliampere, etc. The meter 20 is specially designed so that it gives a steady reading of this average current on a scale calibrated directly in terms of depth such as feet.

The transmitting projector T converts electrical impulses received from the discharge of capacltor 62 in the sounding indicator I, into sound pressure waves, which pass through the water to the bottom and are reflected back to the receiving projector R. Each projector consists of a stack of toroidal nickel laminations, wound with wire through which the electrical impulses pass. Each pack is housed in a coni-cal reflector, which is lled with castor oil and sealed by means of a diaphragm and suitable gasket against leakage.

The electrical impulses set up a magnetic field in the laminations of the transmitting projector, causing the nickel to contract as the leld increases and expand as the field decreases, thus setting up mechanical vibrations or sound pressure waves, which are transferred to the castor oil within the conical reflector. This effect is known as magnetostrictiorr These pressure waves are then reflected, by the conical reflector, in a. parallel-vertical beam; travel through the diaphragm to the bottom where they are reflected back to the diaphragm of the receiving projector. The received sound pressure waves reach the conical reector surrounding the receiver pack and are deflected to the pack to set up vibrations Within the nickel laminations.

'I'he receiver pack differs from the transmitter pack in that it sh-ould be pre-magnetized by a momentary impulse of direct current. Vibrations set up by the sound pressure waves cause contraction and expansion of the pack, a change in the magnetic eld and thus an electrical impulse is generated in the pack winding. This electrical impulse is then transmitted to the primary |10 of transformer |02 in the sounding indicator I through the inter-connecting wiring |'|2 The natural frequency of both packs may be 25.0 kc., which is outside the frequency of interfering noises, such as those caused by ychaiing objects and the like.

Operation of the unit is entirely automatic, requiring only the switching on of the power and an occasional check of the keying rate and calibratlon. A pulse, generated by the blocking oscillator 30, ionizes the gaseous discharge tube (strobotron) 16, thereby discharging the capacitor 82 through the transmitting projector T and initiating the sound pressure wave. The reflected wave, or echo reverts to an electrical impulse, by virtue of the action of the receiving projector R, is amplied by circuit 38 and translated, by means of electronic timing circuit 40, into a. reading of the depth in feet on the depth indication meter 20 in the sounding indicator I.

The principle of operation of the invention has been described, together with apparatus which now is considered to represent the best embodiment thereof, but it shouldbe understood that the apparatus shown is only illustrative and that the invention may be carried out by other means. Certain features oi the invention which are believed to be novel and patentable are defined in the following claims and other inventive features are claimed in the copending application of George T. Lorance, entitled Echo sounding indicator, Serial No. 582,117, filed March 10, 1945.

I claim:

l. In combination, an echo sounding transmitter circuit including means for electronically generating and transmitting pulses at a constant frequency and xed rate, a gas-lled grid-con-l trolled tube, circuit means for impressing said. electronically generated pulses on the input cir cuit of said gas-filled grid-controlled tube causing it to ilre each time a pulse is transmitted, an'echo sounding receiver circuit including a screen-grid vacuum tube amplifier having a screen-grid circuit, a resistance connected in said screen-grid circuit and in the output circuit of said gasfllled grid-controlled tube for reducing the gain of said amplier, when said gas-nlled tube rires, to such an extent that said receiver circuit is incapable of passing pulses transmitted directly from said transmitting means to said receiver circuit, and means for restoring the gainof said amplifier before an echo pulse is received.

2. In combination, an echo sounding transmitter circuit including means for electronically generating and transmitting pulses at a constant frequency and fixed rate, a gas-nlled grid-controlled tube, circuit means for impressing said electronically generated pulses on the input circuit of said gas-filled grid-controlled tube causing it to nre each sime a pulse is transmitted, an echo sounding receiver circuit including a vacuum tube amplier, a resistance connected in a grid circuit of said ampliiler and in the output circuit of said gas-lled grid-controlled tube for reducing the gain of said ampliiier, when said gas-filled tube iires, to such an extent that said receiver circuit is incapable of passing pulses transmitted directly from said transmitting means to said receiver circuit, and means for restoring the gain of said ampliflerbefore an echo pulse is received.

3. In combination, an echo sound transmitter circuit including a blocking oscillator for generating pulses at a fixed rate, a rst' gas-lled grid-controlled tube having'its input connected to the output of said blocking oscillator, a transmitter and a condenser connected in series in the output circuit of said first gas-filled gridfcontrolled tube whereby the firing of said tube by said blocking oscillator causes said condenser to discharge through said tube and said transmitter resulting in the transmission of pulses in timed relation to the pulses generated by said blocking oscillator, a second gas-lled grid-controlled tube having its input connected to the output of said blocking oscillator so as to fire each time said rst gas-lled grid-controlled tube fires, an echo sounding receiver circuit connected to receive and amplify reilected pulses transmitted by said transmitter, said echo sounding receiver circuit including an amplier tube, a resistance connected in a grid circuit of said ampliier tube and in the output circuit of said second gasfilled grid-controlled tube for reducing the gain of said amplier when said second gas-filled gridcontrolled tube fires to such an extent that said receiver is made incapable of transmitting pulses directly transmitted by said transmitter, and means for restoring the gain of said amplier before reflected pulses transmitted by said transmitter are received.

4. A' combination according to claim 3 in which said means for restoring the gain of said amplier comprises a resistance and condenser connected between the anode and cathode of said second gasLfllled grid-controlled tube whereby after a time interval controlled by the rate oi discharge of said condenser, the potential on said anode is reduced to such an extent that said second gas-filled grid-controlled tube ceases to fire.

l 5. In combination, an echo sounding vtransmitter circuit including a blocking oscillator for generating pulses at a xed rate, a rst gasillled grid-controlled tube having its input connected to the output of said blocking oscillator, a transmitter and condenser connected in series in the output circuit of said first gas-nlled gridcontrolled tube whereby the ilring of said tube by said blocking oscillator causes said condenser to discharge through said tube and said transmitter resulting in the transmission of pulses in timed relation to the pulses generated by said blocking oscillator, a second gas-filled grid-con- Y trolled tube having its input connected to the output of said blocking oscillator so as to fire each time said first gas-iilled grid-controlled tube fires.

. an echo sounding receiver circuit connected to receive and amplify reflected pulses transmitted Vby said transmitter, said echo sounding receiver circuit including a screen-grid amplifier tube having a screen grid circuit, a resistance connected in said screen grid circuit and in the output circuit of said second gas-filled grid-controlled tube for reducing the gain of said ampliner when said second gas-lled and grid-controlled tube fires to such an extent that said receiver is made incapable of transmitting pulses directly transmitted by said transmitter and means for restoring the gain of said ampliiier before reilected pulses transmitted by said transmitter are received.

6. A combination according to claim 5 in which said means for restoring the gain of said amplifier comprises a resistance and condenser connected between the anode and cathode of said second gas-lled grid-controlled tube whereby after a time interval controlled by the rate of discharge of said condenser, the potential on said anode is reduced to such an extent that second gas-filled grid-controlled tube ceases to iire.

FRED L. SEEBINGER, JR.

REFERENCES crrnn The '-following references are of record in the ille of this patent:

UNITED STATES PATENTS 

